Resistance:Cotton bollworms and Bt toxins

Derek RussellNatural Resources Institute (UK)

Genetics Dept, University of Melbourne (Australia)

With thanks to

Dr Keshav KranthiCentral Institute for Cotton Research, Nagpur

Resistance

• A genetic change in a population as a result of mortality caused by a chemical or other toxin (e.g.Bt)

• Those organisms with more natural tolerance to the toxin survive and breed and pass on the ability to survive

• In time the whole population becomes able to survive the toxin – they have become resistant!

Antibiotic Resistance

• You have multiplying bacteria in a cut.

• The doctor gives you an antibiotic

• If you don’t take the full dose – the most tolerant bacteria survive and breed quickly

• If you do take the full dose but only once, it is possible that a few bacteria survive to breed

• Therefore you are told to take the full 5 day course at full rates to kill even the tolerant bacteria

Pests of cotton in India

Killed by Bt cotton

• Bollworms - cotton bollworm

- pink bollworm

- spiny bollworm

Not affected

• Leafworms (mostly)

• Aphids• Jassids• Mites

Main pest groups

Bollwormso African/American - Helicoverpa armigera

o Spiny/Spotted - Earias insulana/biplaga

o Pink - Pectinophora gossypiella

Leafwormso Cotton leafworms – Spodoptera sp.

Bt cotton targets

• Cotton bollworm Helicoverpa armigera

181 host plants - 69 crop species

losses - US $ 540 mill annually

• Spiny bollworms - Earias insulana and E. vitella• Pink bollworm - Pectinophora gossypiella

Helicoverpa armigera (American bollworm)(CAB, 1993)

A key pest of cotton and vegetables:

Photos: CIRAD

Cotton bollworm – Helicoverpa armigera

Commercialised transgenic plants resistant to insects

Cotton: 1st commercialised in 1996 -2004: 9 countries;

9.0 mill ha 28% global cotton area 11% of global GMO area

- Insect resistance and herbicide tolerance traits- 25% increase in area from 2003-2004

Maize: 1st commercialised in 1996 -2004 : 8 countries

19.3 mill ha 14% global maize area 23% of global GMO area

- Insect resistance and herbicide tolerance traits- also 25% increase in area from 2003-4

Potato: first commercialised in 1996, withdrawn in 2001

Modified from Giband 2004

Genetically Modified Bt plants

Bt plants have: Gene (DNA) for producing the insecticidal toxin from a soil bacterium

Promotor ‘switches’ on either side of the gene to turn it on and off

Other regulatory genes or introns

May have ‘Marker’ gene used only in the selection process (used to be an antibiotic - kanamycin)

Note:• The plant itself makes the toxin in its tissues using the bacterial gene• The step to turn the pro-toxin into the toxin in the insect gut is not necessary• The gene may be ‘turned on’ more in some tissues than others.

Bacillus thuringiensis (Bt): More than a century of history …

• 1901 : Discovered in silkworm by a Japanese bacteriologist Shigetane ISHIWATA “Sottokin”.

• 1911 : A new isolation by Ernst BERLINER on Ephestia kuehniella (Zeller) larvae from Thuringe (Germany)

Bacillus thuringiensis Berliner

•1938 : First commercial preparation (Sporéine) by Libec Laboratories in France, used

against meal moth Ephestia sp. in flour.

: Bt has been used for more than 65 years as biological insecticide (>90% of the

total biopesticides market).

•1981 : first cloning of a Cry gene

•1985 : First insect resistant transgenic plant

•1990 : First commercialization of a transgenic plant (in China : virus resistant tobacco).

•1995: First Bt transgenic plant commercialised in USA

•2005: more than 81 mill ha of transgenic crops all over the world.

Mode of action of Cry toxins

J-M Vassal - CIRAD

R. A. de Maagd, 2001

Domain III

Domain II

Domain I

Aminopeptidases NCadherins

Mode of action of Cry toxins

Resistance mechanisms for Bt

Resist

Resist Resist

(b) Change solubilisation of the toxin

(c) prevent passage through the peritrophic membrane

(e) Prevent membrane insertion and pore formation

Insects controlled by transgenic plants: Cotton

Toxin Insects controlled Commercial name

Cry1Ac*

(1996)

Bollworms: Cotton, Pink, Spiny Bollgard ® Delta and Pineland/Monsanto

Cry1Ac+

Cry2Ab(2003)

Bollworms: Cotton, Pink, Spiny

Leafworms: Spodoptera spp

Bollgard II ®

Delta and Pineland/Monsanto

Cry1Ac+

Cry1Ab and or CpTi(1997)

Bollworms: Cotton, Pink, SpinyNumerous Varieties

Chinese Agademy of Agric. Sciences

Cry1Ac+

Cry1Fa(2005)

Bollworms: Cotton, Pink, Spiny

Leafworms: Spodoptera spp

WideStrike ®

Dow AgroSciences

Vip3A

(2005?)

Bollworms: Cotton, Pink, Spiny

Leafworms: Spodoptera spp

Cutworms: Agrotis sp …

VipCot ®

Syngenta

Modified from Giband 2004

World Bt cotton adoption – 2003(2004)

Countries with pest complex like India (esp.Helicoverpa armigera)

Country Year

First Bt

Cotton mill ha

Area Bt cotton

% Area under Bt

Insecticide use in

Non-BT

Insecticide use in

BT

% sprays reduced

USA 1996 6.2 2.0 33 5 2 60%

Mexico 1996 0.08 0.028 35 4 2 50%

China 1997 4.8 1.5 51 (66) 20 7-13 50%

Australia 1997 0.4 0.146 36 (58) 11 6 45%

Argentina 1998 0.17 0.009 5 5 2 60%

S. Africa 1998 0.044 0.02 45 (85) 11 4 64%

Indonesia 2001 0.022 0.004 18 9 3 66%

Colombia 2002 0.041 0.004 10 6 2 66%

India 2002 8.5 0.28 3 (10) 14 7 50%

Bt Cotton in China

% of total cotton area

0

10

20

30

40

50

60

70

1997 1998 1999 2000 2001 2002 2003 2004

% of cotton area

GM cotton worldwide in 2005

Bt Cotton

>50,000 ha

Genetic system

Single gene

Double geneTechnology

fee

Argentina Yes Var. Yes Yes

Australia Yes Var. No 1Ac/2AB Yes

China Yes Var. Yes1Ac/(1Ab)

+CpTiNo

Colombia No Var. Yes Yes

India Yes Hybrid Yes(1Ac /2Ab)

coming soonNo

Indonesia No Var. Yes ?

Mexico Yes Var. Yes Yes

S.Africa Yes Var. Yes Yes

USA Yes Var. Yes1Ac+2Ab

(1Ac+1Fa)Yes

Area: 28% of global cotton is GM (9.5mill ha) (herbicide tolerant and insecticidal)

Countries: 9 countries with 59% of world cotton area

Farmers: c 7.2 million (>85% in developing countries – mainly China)

Expected yield improvements with Bt crops

Why?: Pest losses in non-Bt: USA 12%, China 15%

India 60%, Uganda ????

Region Pest pressure

Availability of chemicals

Adoption of Chemicals

Yield effect of GM crops

Developed countries

Low to Med High High Low

Latin America (commercial)

Med Med High Low to Med

China Med Med High Low to MedLatin America (non-commercial)

Med Low to Med Low Med to High

S. and S.E.Asia High Low to Med Low to Med

High

Africa High Low Low High

Qaim and Zilberman - Science (299 p 901) 2003

Target – bollwormsCry1Ac efficacy in current Bt varieties

Efficacy:Spiny bollworms (Earias sps)

Pink Bollworm (Pectinophora gossypiella)

Cotton bollworm (Helicoverpa armigera)

Insecticide use:Global experience gives an average reduction of c.60% in insecticide applications (80% for bollworms)

- Very effective

- Very effective

- Good mid-season- Poor in late season (reduction in bio-availability of

toxin)

Questions?

If toxin expression in Bt plants is not always sufficient to kill bollworms it will select for resistant insects.

• Does Bt cotton give season-long control of caterpillars?

• Are all the parts of the plant equally lethal?

• Are all Bt varieties equally effective?

• What is the chance of resistance to Bt developing?

0

20

40

60

80

100

120

27 40 60 68 75 80 87 96 104 110 116 124 133 138 152 159

Days after sowing

% M

ort

lait

y

Top leaf Middle leaf Bottom leaf Square bract Square bud

H. armigera larval mortality

on Bt-cotton plant partsData from an Indian variety 2003

Kranthi et al 2003

0

1

2

3

4

5

6

Boll rind Boll bract loculi w all raw

cotton

petals sepals anthers ov ary

ug/g

m d

ry w

t

2-BT 20-BT 134-BT 138-BT

144-BT 162-BT 184-BT

Variability in expression of Cry1Ac in plant parts of

commercial Indian hybrids

Bt Hybrids

0

1

2

3

4

5

6

Boll rind Boll bract loculi w all raw

cotton

petals sepals anthers ov ary

ug/g

m d

ry w

t

2-BT 20-BT 134-BT 138-BT

144-BT 162-BT 184-BT

Variability in expression of Cry1Ac in plant parts of

commercial Indian hybridsExpression < 1.8ppm is not sufficient for H.armigera control

_____________________________1.8ppm__

Bt Hybrids

Bt-QuantBt-Quant

Bt-ExpressBt-Express

IS THERE RESISTANCE TO Bt COTTON?

Insects resistant to sprayed Bt

•1990 : Tabashnick et al.– Diamond back moth Plutella

xylostella on cabbage in Hawaï– First case of Bt resistance in the

field following intensive Bt treatments.

• 1985 : McGaughey

-1st case of resistance to Bt - in Meal moth Plodia interpunctella (stock grain population)

Since then cases of resistance have been ONLY in the lab.

Photo - CIRAD

Bt resistance in cotton ?

We have Bt resistance in the lab by :

Heliothis virescens (Tobacco Bollworm) - USAPectinophora gossypiella (Pink Bollworm) - USAHelicoverpa armigera (Cotton Bollworm) – India, China

Helicoverpa armigera : (only in the lab.)

• In India : Kalia et Gujar, 2004

• In Australia : Akhurst et al, 2003

• In China : Xu et al, 2005

• In China : Liang et al, 2000

• In India : Kranthi et al. 2000

• In Africa : Uraichuen 2002

Incompletely dominantAutosomal

In all that works : several cross resistances with the Cry1A family toxins

Incompletely recessiveAutosomal

Completely recessiveSex influenced

Completely dominant, Autosomal

Dominance describe the RS phenotype compare to SS and RR phenotype

One resistance gene with two alleles S and R

SS

RS

RR

In the case of Bt resistance

When RS = SS Resistance is recessive

When RS = RR Resistance is dominant

3 genotypes

Implications of the Indian resistance inheritance system

• Survival on Mech 184 - Bt plants (75-85 days old)

RR two copies of the resistant gene 75%

RS one “ “ “ “ “ 33%

SS no “ “ “ “ “ 5%

• Inheritance - Semi-dominance (0.42 and 0.55 in two populations)

Monitoring of Bt resistance

Survey for the presence of the Bt resistance gene

Screen for possible resistant caterpillars in the cotton

This will warn us before resistance is a major problem and give us time to do something about it.

Is there field resistance to Bt?(field collections of H.armigera from around the country)

LC50 µgCry1Ac/ml diet Regional variability

India2001 Baseline* 0.01 - 0.67 67 fold2002-3 32 fold2003-4 0.04 - 0.38 10 fold

China 1999 Baseline+ 0.091 - 9.093 100 fold

IC50 µgCry1Ac/ml diet Regional variability

1998 & 0.015 – 0.20 13 fold1999 $ 0.016 – 0.099 6 fold2000 $ 0.016 – 0.080 5 fold

Answer

- No definite resistance yet - but it will be difficult to detect by screening for increased survivorship.

- If the truncated cadherin is the major mechanism in China and India we can now screen directly using

molecular tools*

*Kranthi et al 2001; +K.Wu et al 1999; * Y Wu et al. 2005; $K Wu et al 2002

Resistance gene frequency in the field(using F2 screens on field collected insects)

• At least one resistance allele in each group• Frequency is worryingly high for a semi-dominant resistance

Data from K.Kranthi – pers com

Iso-female lines

Frequency of resistance alleles

North 180 0.0075

Centre 195 0.0015

South 210 0.0013

Resistance gene frequency calculated from offspring of field collections - China

Resistance Resistant

AllelePhenotype

FrequencyFrequency

K.Wu 2002 Hebei 0.001 0.004

(moths at traps) Shandong 0.0006 0.002

Y.Wu 2004 Jiangsu 0.004-0.01 0.003

(Bt field survivors)

What is the Bt Resistance Mechanism in H.armigera?

All from survivors in Bt fields additionally laboratory selected

• Chinese H.armigera – cadherin truncation demonstrated (Wu et al 2004)

• Australian H.armigera – unknown binding site mutation (Akhurst et al 2003)

• Indian H.armigera – suggestions of an aminopeptidase involvement and possibly a second mechanism

(Kranthi et al 2004)

– Binding affinity reduced in 6 fold in trypsin activated toxins and 10 fold in protease activated toxins

– Major portion of APN-1 cDNA of Cry1Ac resistant strain sequenced• 16 base substitutions, 6 additions in 2766 nucleotides leading to 17 a.a. differences• One of the these is related to glycosylation (Ser911 to Phe911)

Cadherin disruption

MembraneMembrane

Inside

Outside

Putative Bt toxin Putative Bt toxin binding sitebinding site

Normal Normal cadherincadherin

Truncated Truncated cadherincadherin

How can we manage Resistance?

IRM in the USA

Refuge strategy for India

5 Rows of non-Bt around Bt cotton

Influenced by USA

Arbitrary

Inherent weaknesses

1. Crop manipulation A=Bt cotton

o Rotation: A:B:C:D:E:A:B:C……o Alternation: AAA:BBB:CCC:DDD….o Mosaic: A B C D A C

D A B C Do Refuge: AAAA:00: AAAA:00…..

2. Conserve & encourage natural control

3. Cultural control; Biopesticides; Biological control.

4. ETL based pesticide optimization with selective Insecticides

Potential strategies for conservation of susceptibility

Conditions for effective refugia strategy

Conditions Met in India Met in China

Alleles must be recessive

No Yes

High toxin expression

No – very variable esp in late season

No – very variable esp. in late season

Random mating Probably Probably - due to asynchrony between generations on different hosts

No-fitness deficit No Probably not

Rare resistance alleles

No No

Bt-Adapt*Factors affecting resistance developmentData from EU China work

Genetic factors:• Initial resistant allele frequency

• Dominance

• Mode of inheritance

• Relative survival rate of RR, RS and SS genotypes on Bt and non-Bt plants

• Other factors influencing Hardy-Wienberg

*Kranthi K.R. and Kranthi N.R. (2004) : Modelling adaptability of cotton bollworm Helicoverpa armigera (Hubner) to Bt-cotton in India. Current Science 87(8): 1096-1107

Bt-Adapt (2)Data from published literature

Ecological factors:• Relative host oviposition preference• Host plant availability in the agro-ecosystem• Natural survival on the various hosts• Synchrony between resistant and susceptible genotypes• Relative fitness of the different genotypes on the different hosts• Level and distance of in-season and between-season migration

Control Factors:• Survival after insecticides on Bt and non-Bt hosts• Survival after other mortality on Bt and non-Bt hosts

BT-AdaptStochastic model in Visual Basic

Recursion equations expressing net increases in population density as a function of:

• Fecundity

• Natural survival of life stages

• Survival after insecticide

• Survival after Bt exposure

With survival rates of the 3 genotypes as:

RR – L; RS -Lh+(1-h)K; SS – KWhere h is dominance

Default Parameters for ‘Bt Adapt’

India* China+

Initial frequency of resistant allele ‘R’ 0.0018 .004 - .01

(.0028)

Dominance 0.42 .26

Survival of RR on Bt cotton 1.0 .9; .95; 1.0

Survival of SS on Bt cotton 0.005- 0.05 .001; .01; .05

Survival of RR on conventional cotton 0.97 .97

Emigration rate 0.5 .85

Natural survival – Egg to Larva

“ “ - Larva to Adult

0.08

0.2

.08; .08; .03

.2; .12; .08

Proportion of cotton which is Bt 3% - 40% 99.9%

Mortality from other pest control - Non-Bt cotton

“ “ “ “ “ - Bt cotton

0.5

0.2

.85

.85

*Kranthi et al 2002, 2005 +Zhang and Tang 2002; Y.Wu et al 2005; K.Wu et al 2002 & 2003

Default parameters for H.armigera in Shandong areas in ‘000 ha

Wheat Maize Cotton Soy Peanut Others

Area in ‘000 ha

First 40,000

Second 89 800 20 20 20

Third 4,000 800 2,400 2,400 30

Fourth 5,600 800 2,400 2,400 30

Oviposition Preference

Second 0.05 0.60 0.15 0.1 0.1

Third 0.15 0.47 0.14 0.14 0.1

Fourth 0.37 0.25 0.11 0.11 0.1

Initial frequency of r allele at 1:10,000

Years to r frequency >0.5

0

5

10

15

20

0 0.1 0.2 0.3 0.4 0.5

Initial frequency of r allele

Yea

rsInitial frequency of resistance allele

Actual frequency 0.01

Years to r frequency >0.5

0

10

20

30

40

50

60

0 0.2 0.4 0.6 0.8 1 1.2

Dominance of r allele

Yea

rs

Dominance of resistance gene (0 - fully recessive to 1 - completely dominant)

Actual r=0.26

Years to r frequency >0.5

0

20

40

60

80

100

0 10 20 30 40 50

Ratio of Maize to Cotton area

Yea

rs

Ratio of maize area to cotton areaOviposition preference: Cotton 0.72 Maize 0.28

Pest control efficacy 85% in both

Years to r frequency >0.5

05

101520253035

0 0.2 0.4 0.6 0.8 1 1.2

Ovip. preference for Cotton

Yea

rs

Oviposition preferences on Cotton and Maize Reciprocal – total 1.0

Equal areas of Maize and Cotton. Pest control efficacy 85% in both

Actual = 0.72

Years to r frequency >0.5

0

20

40

60

80

100

0 20 40 60 80 100 120

% of cotton which is Bt

Yea

rsProportion of Cotton which is Bt Cotton

Actual c.99.9%

Years to r frequency >0.5

0

20

40

60

80

100

0 20 40 60 80 100

% control on non-Bt cotton

Yea

rs% H.armigera control on non-Bt cotton

(with 85% control of survivors of Bt cotton)

Years to r frequency >0.5

0

10

20

30

40

50

60

0 20 40 60 80 100 120

% control on Bt cotton

Yea

rs% H.armigera control on Bt cotton survivors

Default 85%

Conclusions on relative importance of variables

Effect – yrs to r >0.5 Significance

Initial frequency of resistance gene

•1/10,000 – 19 yrs•1/100 – 9.3 yrs

Not very major

Dominance of resistance •0.1 – 15.5 yrs•0.9 – 4.8 yrs

Moderate

Proportion of maize to cotton • 1:1 – 4 yrs•10:1 – 15.5 yrs•25:1 - 40 yrs

Strong

Proportion of non-Bt to Bt cotton

•0.1% non-Bt – 9.3 yrs•20% non Bt - 15 yrs•50% non-Bt – 34 yrs

Potentially significant

Pest control in non-Bt cotton With 0.1% non-B cotton:•No control – 88 yrs•85% control – 9.3 yrs

Significant

Pest control in Bt-cotton With 99.9% Bt cotton:•No control – 2.8 yrs•85% control – 9.3 yrs•97% control – 55 yrs

Highly significant

Importance of variablesNon-manageable factors:

1. Initial gene frequency2. Dominance, inheritance pattern etc3. Proportion and oviposition attractiveness of alternate hosts4. Relative survival of RR,RS and SS on Bt and non-Bt cotton5. Proportions of cotton and other hosts

Possible manageable factors:

1. Proportion of cotton which is Bt2. Mortality on non-Bt cotton

Manageable factor:

1. Mortality of Bt cotton survivors The model shows removing carriers of ‘R’ alleles from the field in which they emerge to be the most efficient strategy in preserving susceptibility

Practical strategies?

Restrict Bt area to <40% of cotton? – No Reduce insecticide control efficacy on alternate crops?- No Manage cropping pattern to increase oviposition preference? –

largely impractical Target resistant (RR and RS) genotypes? - Possibly

– Encouragement of bio-control

– Handpicking surviving larvae

– HaNPV –acts best on slow growing larvae

– Insecticides – Applied at population peaks

Summary – possible pest management system in Bt cotton

(insecticide only when thresholds exceeded in crop or other hosts nearby)

Sucking pests

Bollworms

Early Middle Late

Window

Days after sowing

1-75

1

60-75

2

75-90

3

90-110

4

110-140

5

>140

Bio-rational Tolerant genotypes

HaNPV

NeemHaNPV

Insecticides‘Soft’

Seed/stem neo-nicotinyls

Endosulfan Spinosad

Emmamectin

Indoxacarb

‘Hard’ Organo- phosphate

Carbamate

Pyrethroid

Conclusions

Use of the model:• Importance of variables – esp. mortality of

larvae surviving Bt cotton

• Probable trends in resistance with different management practices

• Identifies critical measurements needed for prediction of resistance (e.g. the relative oviposition preference of different crops at different times)

Thank you for your attention

INDIACotton situation

Cotton- 8.7 mill ha- 13 % of world production- 308kg lint/ha mean yield

Insecticide usage in late 1990s - 45% of all insecticides are used

on cotton - 37,000 tonnes of a.i. used on cotton

- 42% of cotton growing costs- 7% p.a. growth in use in the 1990s

INDIA – Bt cotton

Joint venture Monsanto and Maharashtra Seed Company (Mhyco) transforming local hybrids by introgression

1999 - 2002 – successful trials but no approval

2000-2001 – illegal plantings esp. in Gujarat

2002- commercialised – 38,000ha (Mech-162-Bt, Mech 194-Bt, Mech-12-Bt

2004 – Monsanto gene with 3 other companies >500,000ha (6% of crop) and 230,00 framers. Illegal area probably same.

2005 – high performing ‘legal’ material eg Rasi Seeds, and ‘illegal’ material eg Bt-Bunny and Super Bunny

Performance of Bt cotton under trail conditionsOrganised by Company; Supervised by Government; Managed by farmers - 2001

(Qain and Zilberman 2003)

• Maharashtra, Myda Pradesh, Tamil Nadu – 25 districts, 157 farms• Each farmer 1acre Bt; one acre Bt parent; one acre popular local variety• 2001 was a bad year for bollworm attack

2002 season (157 comparisons)

Bt Parent of Bt Popular Check

% difference Bt v. Bt parent

Sucking pest sprays

3.57 3.51 3.45 +1.7%

Bollworm sprays 0.62 3.68 3.43 -83%

Yield (Kg/ha) +s.d.

1,501 833 802 +80%

Performance of Bt cotton under Indian farming conditions2002-2003

(Morse et al 2005)

• Maharashtra – 3 districts, 1,275 villages c.9,000 cotton plots• All farmers with Bt and non-Bt plots

2002 season (7,793 plots) 2003

(1,577 plots)

Non Bt Bt % difference % difference

Seed cost +s.d. Rs 1,138 Rs 3,775 +232% +217%

Sucking pest sprays

2.25 2.24 -0.4% +8%

Bollworm sprays 3.14 1.44 -54% -77%

Seed + Insecticide cost

5,060 5,804 +15% +5%

Yield (Kg/ha) +s.d.

1,510+2,220 2,100+1,000 +39% +63%

Revenue +s.d. Rs 31,081+49,903 Rs 42,948+20,853 +38% +63%

Gross margin +s.d.

Rs 25,730 +49,708 Rs 36,855+20,532 +43% +73%

Performance of Bt cotton divided by district

(Morse et al 2005)

• Maharashtra – 3 districts, 1,275 villages c.9,000 cotton plots• All farmers with Bt and non-Bt plots

Districts Yield % difference Gross Margin % difference

2002 2003 2002 2003

Khandesh +75% +84% +92% +101%

Vidharba +35% +41% +37% +45%

Marathwada +18% +60% +14% +68%

Parts of Andhra Pradesh in 2004 had poor yields with Bt cotton – possibly varietal

Conclusions from IndiaConclusions from India

Commercialisation processCommercialisation process

• Government handling of approval Government handling of approval process was poorprocess was poor

• Hybrid release - maximised IPR Hybrid release - maximised IPR control and company profits control and company profits butbut sales of F2 and F3 material has sales of F2 and F3 material has compromised efficacy and compromised efficacy and threatended susainabilitythreatended susainability

EfficacyEfficacy• Excellent control of pink and spiny Excellent control of pink and spiny

bollwormsbollworms

• Inadequate control of cotton Inadequate control of cotton bollworm in the late seasonbollworm in the late season

Farmer suitabilityFarmer suitability

• Saves labourSaves labour

• Yield increase 40-60% (80% in Yield increase 40-60% (80% in bad bollworm years bad bollworm years (Qaim 2003)(Qaim 2003)

• Benefit very variable with area, Benefit very variable with area, season and varietyseason and variety

ButBut• Large amounts of poor and Large amounts of poor and

unauthorised materialunauthorised material

• There is a continuing need for IPM There is a continuing need for IPM trainingtraining

Main points

Bt cotton Advantages Good control of bollworms No field resistance yet Little impact on beneficials Bollworm insecticides decline c.80% Yield rises more (<80%) in lower input situations Profitability is strongly enhanced

But….. Results vary with bollworm pressure, germplasm and quality control Late season control of Helicoverpa armigera is not good Countries paying technology fees have smaller margins Having Bt in appropriate germplasm is crucial